A spin-transfer-torque type MRAM is expected to enable both shrinking of a cell size and reduction of a writing current.
An in-plane magnetization type magnetoresistive effect element which has been mainly studied generally utilizes shape magnetic anisotropy. In this case, in order to increase the magnetic anisotropic energy of a magnetic layer, countermeasures need to be taken of increasing an aspect ratio of a magnetoresistive effect element, increasing the film thickness of a recording layer or increasing the saturation magnetization of the recording layer. However, when characteristics of the spin-transfer-torque type are taken into account, these countermeasures cause an increase in a magnetization inversion current and therefore are not suitable for the shrinking of elements.
Further, the in-plane magnetization type magnetoresistive effect element utilizes magnetic anisotropy which is exhibited depending on a shape, and therefore a magnetization inversion current is susceptible to the variability of the shape. As a result, if the variability of the shape increases following shrinking, the variability of the inversion current increases.
By contrast with this, it is considered to use for a ferromagnetic material for forming a magnetoresistive effect element a perpendicular (vertical) magnetization film which has magnetic anisotropy in the direction perpendicular to a film surface.
In case where crystal magnetic anisotropy of a magnetic layer is utilized for a perpendicular magnetization type magnetoresistive effect element, shape anisotropy of an element (magnetic layer) is not utilized, so that it is possible to make the shape of the element smaller than the in-plane magnetization type. Further, the perpendicular magnetization type magnetoresistive effect element can reduce dispersion in an easy direction of magnetization. Hence, by adopting a material having a large crystal magnetic anisotropy, the perpendicular magnetization type magnetoresistive effect element is expected to realize both of shrinking and a lower current while maintaining thermal disturbance resistance (heat resistance).
In order to put MRAM into practical use, the element characteristics of the perpendicular magnetization type magnetoresistive effect element need to be improved. Further, the perpendicular magnetization type magnetoresistive effect element is also demanded to be resistant against a high temperature process in a manufacturing process.